1. Field of the Invention
This invention relates to a sheet feeding apparatus capable of feeding sheets separately sheet by sheet and to a sheet feeding apparatus used for an image forming apparatus such as, e.g., a photocopier or a facsimile machine.
2. Description of Related Art
As a sheet feeding apparatus used for conventional facsimile machines, for example, there is an apparatus for separately feeding sheet by sheet a bundle of original documents mounted on a tray. In such a sheet feeding apparatus, if the bundle of the original documents is placed in an excessively deep portion when the bundle of the original documents are set, the bundle of the original document cannot be separated, and so called xe2x80x9cmultiple feedingxe2x80x9d, in which two or more sheets of the original documents are fed at a time, may occur. Therefore, some conventional sheet feeding apparatuses frequently have a mechanism to prevent excessively deep placement of the original documents, to effectuate separation capability for the original document bundle.
In most cases of conventional apparatuses, however, their constitutions were complicated and increased greatly their costs. To solve this problem, a mechanism as set forth in Japanese Unexamined Patent Publication, Heisei, No. 9-58891 and Japanese Unexamined Patent Publication, Heisei No. 9-58892 was proposed as an inexpensive mechanism for preventing the original documents from excessively deep placed.
In the above mechanism, a stopper for preventing excessively deep placement (excessive insertion) of original documents is pivotally moved from a limiting position for limiting front end of the original documents to an escape position for releasing the limitation in utilizing rotation of a conveyance roller, and comes back from the escape position to the limiting position by its weight.
However, the above conventional apparatus did not have any consideration to relation between timing for start of feeding the original documents and timing for releasing the limitation of the stopper. That is, when the separation roller for separately feeding the original documents begins to rotate earlier than release of the limitation at the original documents by the stopper, the front end of the original documents to be fed by the separation roller is pushed onto the stopper located at the limiting position, thereby causing conveyance failures such that the front end of the original documents is folded or that the original documents are fed obliquely.
In a case of such a conventional mechanism, while the conveyance roller rotates, the stopper repeats pivotal movements between the limiting position and the escape position. When a user inadvertently sets the original documents without striking the original documents (specially, thin original documents) to the stopper, the front end of the original documents does not reach the stopper yet (located on an upstream side in the conveyance direction) when the stopper pivotally moved to the escape position upon the start of the feeding of the original documents, and therefore, a situation may occur in which the front end reaches the stopper after the stopper comes down to the limiting position. Under this situation, the front end of the original documents strikes the stopper, a conveyance failure that the front end of the original documents would be folded may occur.
It is an object of the invention to prevent conveyance failures such as folding of sheets or like occurring due to striking of the front end of the sheets to a stopper when or after the sheet conveyance starts.
A representative structure of the invention to accomplish the above object comprises a feeding means for feeding sheets, and a limiting means movable between a limiting position for limiting a front end of the sheets and an escape position for releasing the limitation, wherein the limiting means releases the limitation on the front end of the sheets before the sheets start to be fed.
According to the above structure, before the sheets start to be fed, the limiting means releases the limitation on the front end of the sheets, so that conveyance failures such that the front end of the sheets is folded may be prevented.
Since the limiting means is moved to the escape position before the sheets start to be fed, start timing of feeding the sheets can be delayed by providing a delaying means between a driving means and a first feeding means. More specifically, the delaying means is constituted of two rotary members, in which projections arranged in the same track on a surface facing with each other are engaged to transmit drive force from a drive source, as well as in which the projections arranged at two rotary bodies have a play between the projections for delaying the start of drive by means of the play.
According to the above structure, the limiting means releasing the limitation on the front end of the original documents is held in a state to release the limitation until that the front end of the sheets is fed at least on the downstream side in the conveyance direction of the limiting means. Therefore, for example, even if a user inadvertently sets sheets (particularly, thin sheets) as not reaching the limiting means, the apparatus can prevent conveyance failures such that the front end of the sheets is fold upon striking the limiting means.
More specifically, for example, as the feeding means, it is constituted of a first feeding means for separately feeding sheet by sheet sheets inserted from an insertion opening, and a second feeding means arranged on the downstream side in the conveyance direction of the first feeding means for starting rotation earlier than the first feeding means, and the limiting means is movable to the escape position for releasing the limitation on the front end in accordance with the rotation of the second feeding means, so that the apparatus, though with a simple structure, can receive the above advantages.
The limiting means is a pivotal member that can make pivotal upward movements and is moved pivotally to the escape position located on an upper side in accordance with the rotation of the second feeding means and moved down to the limiting position by its weight, so that the apparatus can realize switching of limiting and releasing modes for the front end of sheets with such a simple structure.
The limiting means is a pivotal member having a limiting portion on the upstream side in the conveyance direction of a pivotal shift and having a protecting portion on the downstream side in the conveyance direction. When a projecting portion of the second feeding means pushes down the projecting portion, the limiting portion of the limiting means is pivotally moved to the upper escape position, and the projecting portion of the second feeding means pushes down the projecting portion of the limiting means before the start of the sheet conveyance and continuously pushes down the projecting portion of the limiting means until that at least the front end of the sheets is fed on the downstream side in the conveyance direction of the limiting means. With this structure, the apparatus can reduce the number of parts and the costs and, with such a simple structure, prevent conveyance failures such that the front end of the sheets is fold upon striking the limiting means.
Moreover, an image forming apparatus having at least a reading means for reading images on sheets to be read is characterized in having the sheet feeding apparatus thus structured as a feeding means for feeding sheets to be read to the reading means.